Interleukin-17A (IL-17A, synonymous with IL-17) is a cytokine produced from the TH17 lineage of T cells. IL-17 was originally designated “CTL-associated antigen 8” (CTLA-8) when cloned from a rodent T cell hybridoma and identified as a protein having amino acid sequence homology with the thirteenth open frame (ORF-13) of herpesviurs saimiri, a γ herpes virus that causes T cell lymphoma in monkeys and rabbits (Rouvier et al., J. Immunol., 150 5445-5556 (1993); Yao et al., Immunity, 3: 811-821 (1995)). The human equivalent of CTLA-8 was later cloned and designated “IL-17” (Yao et al., J. Immunol., 155(12): 5483-5486 (1995); Fossiez et al., J. Exp. Med., 183(6): 2593-2603 (1996)). The human gene for IL-17 encodes a 155 amino acid polypeptide comprising a 19 amino acid signal sequence and a 132 amino acid mature domain.
Human IL-17A is a glycoprotein with a Mr of 17,000 daltons (Spriggs et al., J. Clin. Immunol., 17: 366-369 (1997)). IL-17A may exist as either a homodimer or as a heterodimer complexed with the homolog IL-17F to form heterodimeric IL-17A/F. IL-17F (IL-24, ML-1) shares a 55% amino acid identity with IL-17A. IL-17A and IL-17F also share the same receptor (IL-17R), which is expressed on a wide variety of cells including vascular endothelial cells, peripheral T cells, B cells, fibroblast, lung cells, myelomonocytic cells, and marrow stromal cells (Kolls et al., Immunity, 21: 467-476 (2004); Kawaguchi et al., J. Allergy Clin. Immunol., 114(6): 1267-1273 (2004); Moseley et al., Cytokine Growth Factor Rev., 14(2): 155-174 (2003)). Additional IL-17 homologs have been identified (IL-17B, IL-17C, IL-17D, IL-E). These other family members share less than 30% amino acid identity with IL-17A (Kolls et al., 2004).
IL-17A is involved in the induction of proinflammatory responses and induces or mediates expression of a variety of other cytokines, factors, and mediators including tissue necrosis factor-alpha (TNF-α), IL-6, IL-8, IL-1β, granulocyte colony-stimulating factor (G-CSF), prostaglandin E2 (PGE2), IL-10, IL-12, IL-1R antagonist, leukemia inhibitory factor, and stromelysin (Yao et al., J. Immunol., 155(12): 5483-5486 (1995); Fossiez et al., J. Exp. Med., 183(6): 2593-2603 (1996); Jovanovic et al., J. Immunol., 160: 3513-3521 (1998); Teunissen et al., J. Investig. Dermatol., 111: 645-649 (1998); Chabaud et al., J. Immunol. 161: 409-414 (1998)). IL-17 also induces nitric oxide in chondrocytes and in human osteoarthritis explants (Shalom-Barak et al., J. Biol. Chem., 273: 27467-27473 (1998); Attur et al., Arthritis Rheum., 40: 1050-1053 (1997)).
Through its role in T cell mediated autoimmunity, IL-17 induces the release of cytokines, chemokines, and growth factors (as noted above), is an important local orchestrator of neutrophil accumulation, and plays a role in cartilage and bone destruction. There is growing evidence that targeting IL-17 signaling might prove useful in a variety of autoimmune diseases including rheumatoid arthritis (RA), psoriasis, Crohn's disease, multiple sclerosis (MS), psoriatric disease, asthma, and lupus (SLE) (see, e.g., Aggarwal et al., J. Leukoc. Biol., 71(1): 1-8 (2002); Lubberts et al., “Treatment with a neutralizing anti-murine interleukin-17 antibody after the onset of collagen-induced arthritis reduces joint inflammation, cartilage destruction, and bone erosion,” Arthritis Rheum., 50: 650-659 (2004)).
The pathogenic role of TNF in arthritis is well established as TNF-α antagonists reduce inflammation and limit progression of cartilage damage and bone erosion in human disease (van den Berg. “Anti-cytokine therapy in chronic destructive arthritis,” Arthritis Res., 3: 18-26 (2001)). Although TNF antagonists have revolutionized RA therapy, a significant portion of patients do not respond adequately to these drugs. Preclinical studies with TNF-α and IL-17 point to both independent and overlapping roles in arthritis pathophysiology. Whereas IL-17 or TNF-α alone exert only modest effects on proinflammatory gene expression, the combination of IL-17 with TNF-α leads to strong synergistic responses. This synergy results in upregulation of cytokines (LeGrand et al., Arthritis Rheum., 44: 2078-2083 (2001)) and proinflammatory chemokines (Chabaud et al., J. Immunol., 167: 6015-6020 (2001)) and also in the induction of cartilage and bone destruction (Van Bezooijen et al., Ann. Rheum. Dis., 61: 870-876 (2002)). Interaction between TNF-α and IL-17 has been demonstrated as a predicting factor for joint damage progression in humans in a two-year prospective study of RA patients (Kirkham et al., Arthritis Rheum., 54: 1122-1131 (2006)). In addition, IL-17 mRNA levels correlate poorly with TNF-α expression in RA, indicating that IL-17 blockade might complement TNF-α antagonists for optimal treatment of RA (Kohno et al., Mod. Rheumatol., 18: 15-22 (2008)).
Although a variety of antibodies to IL-17 have been described in the nearly two decades of work since the discovery of this critical proinflammatory cytokine, there remains a need for improved antibodies that can effectively mediate or neutralize the activity of IL-17 in the inflammatory response and autoimmune disorders.